Abstract: In distributed coherent aperture radar system, different transmitting signals from each unit radar are synthesized at target, where the coherent parameters including the time and phase offsets are key parameters for the realization of full coherence in distributed coherent aperture radar. In this paper, a coherent parameters estimation method for a moving target through Kalman smoothing was proposed. Firstly, the radar local coordinates and the target coordinates were described. The moving model of target and the mathematical expression of coherent parameters were presented. Then, an estimation method of coherent parameters based on orthogonal signals was given. After establishing the state and measurement mathematical model, a novel coherent parameters estimation method using Kalman filter was proposed to improve the estimation accuracy of coherent parameters. Finally, the simulations were carried out to illustrate the performance of proposed methods.